Fabrication of gold nanowires in micropatterns using block copolymers

Ethanol Oxidation Reaction Mechanism on Gold Nanowires from Density Functional Theory

Thin gold nanowires (NWs) are materials that could be used as support in different chemical reactions. Using density functional theory (DFT) it was shown that NWs that form linear atomic chains (LACs) are suitable for stimulating chemical reactions. To this end, the oxidation reaction of ethanol supported on the LACs of Au-NWs was investigated. Two types of LACs were used for the study, one pure and the other with an oxygen impurity. The results showed that the oxygen atom in the LAC fulfills important functions throughout the reaction pathway. Before the chemical reaction, it was observed that the LAC with impurity gains structural stability, that is, the oxygen acts as an anchor for the gold atoms in the LAC. In addition, the LAC was shown to be sensitive to disturbances in its vicinity, which modifies its nucleophilic character. During the chemical reaction, the oxidation of ethanol occurs through two different reaction paths and in two stages, both producing acetaldehyde (CH₃ CHO). The different reaction pathways are a consequence of the presence of oxygen in the LAC (oxygen conditions the formation of reaction intermediates). In addition, the oxygen in the LAC also modifies the kinetic behavior in both reaction stages. It was observed that, by introducing an oxygen impurity in the LAC, the activation energy barriers decrease ∼69 % and ∼97 % in the first and second reaction stages, respectively.

Self-assembly, alignment, and patterning of metal nanowires

Armed with the merits of one-dimensional nanostructures (flexibility, high aspect ratio, and anisotropy) and metals (high conductivity, plasmonic properties, and catalytic activity), metal nanowires (MNWs) have stood out as a new class of nanomaterials in the last two decades. They are envisaged to expedite significantly and even revolutionize a broad spectrum of applications related to display, sensing, energy, plasmonics, photonics, and catalysis. Compared with disordered MNWs, well-organized MNWs would not only enhance the intrinsic physical and chemical properties, but also create new functions and sophisticated architectures of optoelectronic devices. This paper presents a comprehensive review of assembly strategies of MNWs, including self-assembly for specific structures, alignment for anisotropic constructions, and patterning for precise configurations. The technical processes, underlying mechanisms, performance indicators, and representative applications of these strategies are described and discussed to inspire further innovation in assembly techniques and guide the fabrication of optoelectrical devices. Finally, a perspective on the critical challenges and future opportunities of MNW assembly is provided.

Liquid Phase Infiltration of Block Copolymers

Novel materials with defined composition and structures at the nanoscale are increasingly desired in several research fields spanning a wide range of applications. The development of new approaches of synthesis that provide such control is therefore required in order to relate the material properties to its functionalities. Self-assembling materials such as block copolymers (BCPs), in combination with liquid phase infiltration (LPI) processes, represent an ideal strategy for the synthesis of inorganic materials into even more complex and functional features. This review provides an overview of the mechanism involved in the LPI, outlining the role of the different polymer infiltration parameters on the resulting material properties. We report newly developed methodologies that extend the LPI to the realisation of multicomponent and 3D inorganic nanostructures. Finally, the recently reported implementation of LPI into different applications such as photonics, plasmonics and electronics are highlighted.

A Single Crystal 2D Hexagonal Array in a Centimeter Scale with a Self-Directed Assembly of Diblock Copolymer Spheres

The creation of a single-grain two-dimensional (2D) nanoarray over a large area (∼1 cm²) has been only realized with expensive lithographic fabrication involving a complicated multichemical process. In this work, we report the production of a highly aligned single-grain 2D crystalline nanoarray over a centimeter-scale large area with a concept of self-directed assembly (SDA) in block copolymer (BCP) thin films. No lithographic guiding pattern is employed in SDA. A sphere-forming BCP is first transformed to transient-cylinders and aligned with shear. The aligned cylinders act as a guiding pattern to restore the sphere-morphology producing a single-grain 2D crystalline array with the following solvent vapor annealing. The SDA process has two governing parameters: orientational order of guiding patterns in the first step and the lattice matching between the transient guiding cylinders and the restored spheres. The successful application of SDA yields a single-grain of 2D crystalline hexagonal nanoarray with an exceptional long-range order, which is confirmed by employing image treating algorithms and grazing incidence small-angle X-ray scattering (GISAXS) measurements. The suggested SDA strategy is found to be effective for large-scale nanopatterning with no lithographic tools.

Chiral Plasmonic Nanowaves by Tilted Assembly of Unidirectionally Aligned Block Copolymers with Buckling-Induced Microwrinkles

Chiral-structured nanoscale materials exhibit chiroptical properties with preferential absorptions of circularly polarized light. The distinctive optical responses of chiral materials have great potential for advanced optical and biomedical applications. However, the fabrication of three-dimensional structures with mirrored nanoscale geometry is still challenging. This study introduces chiral plasmonic nanopatterns in wavy shapes based on the unidirectional alignment of block copolymer thin films and their tilted transfer, combined with buckling processes. The cylindrical nanodomains of polystyrene-block-poly(2-vinylpyridine) thin films were unidirectionally aligned over a large area by the shear-rolling process. The aligned block copolymer thin films were transferred onto uniaxially prestrained polydimethylsiloxane films at certain angles relative to the stretching directions. The strain was then released to induce buckling. The aligned nanopatterns across the axis of the formed microwrinkles were selectively infiltrated with gold ions. After reduction by plasma treatment, chiral plasmonic nanowave patterns were fabricated with the presence of mirror-reflected circular dichroism spectra. This fabrication method does not require any lithography processing or innately chiral biomaterials, which can be advantageous over other conventional fabrication methods for artificial nanoscale chiral materials.

Shear-solvo defect annihilation of diblock copolymer thin films over a large area

Achieving defect-free block copolymer (BCP) nanopatterns with a long-ranged orientation over a large area remains a persistent challenge, impeding the successful and widespread application of BCP self-assembly. Here, we demonstrate a new experimental strategy for defect annihilation while conserving structural order and enhancing uniformity of nanopatterns. Sequential shear alignment and solvent vapor annealing generate perfectly aligned nanopatterns with a low defect density over centimeter-scale areas, outperforming previous single or sequential combinations of annealing. The enhanced order quality and pattern uniformity were characterized in unprecedented detail via scattering analysis and incorporating new mathematical indices using elaborate image processing algorithms. In addition, using an advanced sampling method combined with a coarse-grained molecular simulation, we found that domain swelling is the driving force for enhanced defect annihilation. The superior quality of large-scale nanopatterns was further confirmed with diffraction and optical properties after metallized patterns, suggesting strong potential for application in optoelectrical devices.

Theoretical investigation on the electronic structure of one dimensional infinite monatomic gold wire: insights into conducting properties

Mixed-valence metal–organic nanostructures show unusual electronic properties. In our pervious investigation, we have designed and predicted a unique one-dimensional infinite monatomic gold wire (1D-IMGW) with excellent conductivity and the interesting characteristic of mixed valency (Au_c³⁺ and Au⁰_i). For further exploring its conduction properties and stability in conducting state, here we select one electron as a probe to explore the electron transport channel and investigate its electronic structure in conducting state. Density functional theory (DFT) calculations show the 1D-IMGW maintains its original structure in conducting state illustrating its excellent stability. Moreover, while adding an electron, 1D-IMGW is transformed from a semiconductor to a conductor with the energy band mixed with Au_c (5d) and Au_i (6s) through the Fermi level. Thus 1D-IMGW will conduct along its gold atom chain demonstrating good application prospect in nanodevices.

The electron transport is along the energy band mixed with Au_c (5d) and Au_i (6s) through the Fermi level for [1D-IMGW]⁻.